A lot off Ti:LiNbO2 opticnl planar waveguides has been fabricated on X, Y, Z-cut crystals in dry and wct atmosphere flowing water vapor to the Oz gas. Optical and structural parameters have been measured, and the effects of water vapor investigated. The results obtained show importants dependences of water vapor and optical properties (mode number·, mode effective indcx, . .. l and estructural characteristics (titanium profi les, spectrum of species, .. ). The diffusion parameters are always rather more influencied by extraordinary than by ordinary polarizations. In general the great dependence is observed in Z-cut substrates.